The present invention concerns a catalytic composition and a process using this composition for the disproportionation (also known as metathesis) of olefins. This composition is produced by dissolving a tungsten and/or molybdenum compound in an ionic liquid mixture of a quaternary ammonium halide and/or a quaternary phosphonium halide, an aluminium halide, and an aluminium alkyl compound.
Olefin disproportionation is readily catalysed by typically heterogeneous catalysts such as molybdenum, tungsten or rhenium oxides deposited on silica or alumina, or by organometallic catalysts known as homogeneous catalysts, produced by combining halides or substituted halides of tungsten and molybdenum with organometallic compounds from the principal series, more particularly organic aluminium compounds. Different organometallic systems have been described by H. T. Dodd and K. J. Rutt in Journal of Molecular Catalysis, 15, 1982, pp 103-110.
More recently, J. M. Basset et al, in U.S. Pat. No. 4,550,216, have shown that in a chlorobenzene medium, the product of the interaction of a halogenated tungsten compound containing two phenoxo groups which are themselves substituted by electronegative groups in the ortho positions, with organometallic compounds from the principal series was particularly active in olefin metathesis catalysis. The problem with the system, however, was that it was not possible to exploit the full capabilities of the catalyst before its destruction.
U.S. Pat. No. 5,104,840 describes a liquid composition of ionic character produced by bringing quaternary ammonium halides and/or quaternary phosphonium halides into contact with alkyl aluminium dihalides and, optionally, an aluminium trihalide. This patent describes the use of these media as solvents for transition metal complexes, in particular nickel complexes which do not contain a carbon-nickel bond, which are transformed into olefin oligomerisation catalysts. The use of such media, which are not miscible with aliphatic hydrocarbons, in particular with the products of olefin transformation, results in better separation of the products and improves the use of homogeneous catalysts. In the following description, these media are termed "molten salts" since they are liquid at moderate temperatures.
We have now discovered that tungsten or molybdenum halides substituted with one or two phenoxo groups containing at least two hydrocarbon substituents in the ortho, ortho' positions, when dissolved in "molten salts", are effective olefin disproportion catalysts. This formulation has proved to be of particular interest since the tungsten or molybdenum complexes dissolved therein are insoluble in olefins, have a high catalytic activity and can be used over the whole of the active period.